SuperAntispyware has a free and a paid version, so it passes my first test of being a free application that works well. The paid version also has a realtime scanner and scheduler that compares to Spybot's TeaTimer, or Windows Defender.
One of the best reasons for using SuperAntispyware is the fact that it actually can help remove some of the nastiest malware that has been released including the variety of Zlob trojan infections, Vundo infections, and more. Before I started using this program, I had to resort to specialized removal tools and a lot of manual techniques to rid some computers of these pests. Now, I run SuperAntispyware and then check what's left to remove. In many cases, the program has done most of the work for me.
Its also easy to use. You'll notice the main menu of the program below. You can scan your hard drive, check for updates to the program, find out what's in quarantine, and check the dates of your last scan and update. With the paid version you can also schedule your scanning and have realtime protection against spyware infections.
SuperAntispyware has impressed me so much that its now one of the first tools I use to remove problems on a computer. It's one of the only tools that can remove some infections by itself, and the creators of the program seem to update it on a regular basis.
Go download and try it out for yourself